1. Field of the Invention
This invention relates to syringe systems that are used for controlling and monitoring conditions of inflation or deflation of a balloon-tipped catheter, and more particularly to a reusable and detachable electronic module used to electronically monitor the syringe system, or to provide electronic data used to monitor the syringe system.
2. The Present State of the Art
Balloon-tipped catheter systems have been known and used in the medical arts for a number of years in connection with a variety of different kinds of procedures which are used, for example, in various fields of medicine, such as urology, gynecology, cardiology and others. Particularly in connection with the treatment of coronary artery disease, the use of balloon-tipped catheters and their associated syringe systems have become widely used.
Coronary artery disease is the narrowing of the arteries that feed oxygen-rich blood to the heart. Since the heart is a muscle whose primary job is to pump oxygenated blood throughout the body, the heart needs adequate amounts of oxygen to properly function. Thus, when the coronary arteries which are located on the top of the heart and through which oxygenated blood is returned to the heart become narrowed or blocked (a condition known as "stenosis"), angina can result. Angina is a symptom of coronary artery disease characterized by chest pain or pressure that can radiate to the arm or jaw, and is caused by a lack of oxygen-rich blood to the heart muscle. Coronary artery disease with its accompanying symptom of angina results from atherosclerosis, which is a build up of waxy material called plaque inside the arteries. When this happens, under exertion or stress, the heart demands more oxygen but the narrowed coronary arteries cannot supply enough oxygen-rich blood to meet the demand, resulting in angina. Unless corrected, this condition can lead to a fatal heart attack.
Initially, there were two basic ways to treat coronary artery blockages: with medicine or by performing coronary artery by-pass surgery. Various kinds of medication could be administered which would decrease the work of the heart by slowing the heart rate, dilating the blood vessels, or lowering blood pressure. However, such medicinal treatment did not cure coronary artery blockage, which thus remained and which would therefore continue to present a risk that at some point the blockage would become serious enough to require surgical intervention.
In coronary artery by-pass surgery, a blood vessel from the chest or leg is grafted beyond the point of blockage so that the blood detours past the blockage in order to reach the heart. In some severe cases, multiple by-passes are performed. As is well known, coronary artery by-pass surgery is expensive, is a high risk procedure and often requires prolonged hospitalization and recovery periods.
Later on, another method for treating coronary artery disease was developed, called balloon coronary angioplasty, or more technically, percutaneous transluminal coronary angioplasty (PTCA). PTCA is a much less traumatic procedure than coronary artery by-pass surgery. PTCA takes about two hours and can be done under local anesthesia, with the result that often a patient can be back on his feet and active in a matter of days. Because PTCA is much less expensive and less traumatic than by-pass surgery and yet in many cases still effectively removes blockage, PTCA has experienced a dramatic increase in the number of such procedures performed each year. Since coronary artery disease remains the number one cause of death, PTCA may be expected to continue to play an important role in the treatment of coronary artery disease.
In performing PTCA, an introducer sheath is inserted through an incision made in the groin or arm area and into the corresponding artery of, such as the femoral artery. An x-ray sensitive dye is injected into the coronary artery through a catheter that is introduced through the sheath. The dye enables the doctor, through the use of real time x-ray techniques, to clearly view the arteries on a television monitor and to thereby locate the artery blockage. A balloon-tipped catheter with a guide wire at the end of it is then advanced through the artery to the point of the blockage with the help of the x-ray monitor.
As schematically illustrated in FIGS. 1A-1C, the balloon catheter 10 is advanced to the middle of the blockage 12. The catheter 10, which is filled with a fluid and is coupled at its other end to an inflation syringe, is manipulated by the cardiologist. Once the balloon catheter is in place, utilizing the inflation syringe the balloon is inflated for 20 to 60 seconds as shown in FIG. 2B. The balloon is then deflated to permit sufficient blood flow to the heart and this procedure is then repeated typically several times to compress the plaque on the arterial wall, as shown in FIG. 1C. After the results are checked, the balloon catheter and guide wire are then removed.
As will be appreciated, notwithstanding that PTCA is a much less traumatic procedure than coronary artery by-pass surgery, nonetheless exacting control with respect to inflation pressure, and duration of the inflation and deflation periods is essential to the safety of the patient. For example, when the balloon catheter is completely inflated so as to begin compressing the plaque, blood flow to a region of the heart is thereby temporarily shut off. This creates a condition known as myocardial ischemia, which can initiate cardiac arrest. Accordingly, the pressure exerted on the artery by the balloon catheter as well as the duration of the blockage created by inflating the balloon catheter must both be carefully controlled by the attending cardiologist and other personnel. The inflation pressures and duration of each inflation and deflation must be based on the cardiologist's assessment of the health of the patient and the patient's ability to withstand such a temporary stoppage of blood flow to the heart.
In the past, PTCA syringe systems have been equipped with standard analog or Bourdon-tube gauges that are utilized to sense and read the pressure used for purposes of inflating a balloon catheter. Human observation of stop clocks and the like has been used to control the duration of the inflation and deflation.
While these prior art techniques have been widely used with success, there is still a serious risk of human error when using such systems. The gauges used on such syringe systems are often awkward and difficult to accurately read, and are also subject to malfunction. Thus, improper recording of inflation pressure and/or duration of either inflation or deflation may occur. Accordingly, there is a need for the cardiologist and/or clinician to be able to improve the degree of control and precision with respect to monitoring of PTCA data. There is also a need to be able to accurately record the PTCA data so that in the event of any later question with respect to whether the procedure was properly carried out, there is an accurate record from which to answer such questions.
Many types of syringe inflation systems have been proposed or used in the art which, to varying degrees, provide for more careful monitoring and/or recording of PTCA data. Two of the first commercially successful syringe inflation systems which provided digital monitoring of PTCA data are the Intellisystem.RTM. and Monarch.RTM. syringe inflation systems of Merit Medical Systems, Inc., which are produced and sold under U.S. Pat. Nos. 5,135,488 and 5,201,753 (hereinafter the "'488" and "'753" patents) respectively.
The Intellisystem.RTM. syringe inflation system provides an inflation syringe with an attached semiconductor transducer mounted to the syringe barrel. The transducer output is connected by an electrical cable to a bedside monitor that digitally processes the transducer signal to provide a digital readout of various PTCA data, including the magnitude of each inflation and deflation and the duration of each inflation and deflation. The Monarch.RTM. syringe inflation system provides an inflation syringe that has a miniaturized digital monitor mounted to the syringe barrel in an integral fashion.
After the PTCA procedure is complete, with the Intellisystem.RTM. syringe inflation system, the inflation syringe with its attached transducer is disposed of. In the case of the Monarch.RTM. syringe inflation system, the syringe with the attached miniature monitor is all completely disposed of.
There is great concern in the health care industry for keeping health care costs as low as possible. Thus, there is an ongoing need to find ways of providing syringe inflation systems which, like the Intellisystem.RTM. and Monarch systems.RTM., are effective for monitoring PTCA data, but which are also less costly and minimize disposal of costly components. The present invention addresses this need.